This issue is caused by the fact that your image consists of a black icon on top of a black background. The background is normally hidden by the alpha (transparency) channel, but in your case I assume you converted using “true color” mode which ignores the alpha channel.
There are two ways to fix this:
- Convert using “true color with alpha” mode.
- Edit the image in GIMP or a similar tool to replace the transparent parts with a white background, then convert using “true color” mode.